Panel construction



Dec. 5, 1961 A. F. ENSRUD EI'AL PANEL CONSTRUCTION 5 Sheets-Sheet 1Filed July 13, 1959 uwuvrons ALF F. ENSRUD MARIO L. OCHIEANO Dec. 5,.1961 A. F. ENSRUD ETAL PANEL CONSTRUCTION 5 Sheets-Sheet 2 Filed July13, 1959 mmvroxs ALF E ENSRUD MARIO L.OCHIEANO Dec. 5, 1961 A. F. ENSRUDETAL 3,011,602

PANEL CONSTRUCTION Filed July 13, 1959 5 Sheets-Sheet s Dec. 5., 1961 A.F. ENSRUD ElAL PANEL CONSTRUCTION 5 Sheets-Sheet 4 Filed July 13, 1959Ail;

Dec. 5, 1961 A. F. ENSRUD ETAL PANEL CONSTRUCTION 5 Sheets-Sheet 5 FiledJuly 13, 1959 INVENTORj 41/ 2. 145 900 W400! QW/MA/d United StatesPatent 3,011,602 PANEL CONSTRUCTION Alf F. Ensrud, North Hollywood, andMario L. Ochieano,

Burbank, Calif, assiguors to Lockheed Aircraft Corporation, Burbank,Calif.

Filed July 13, 1959, Ser. No. 826,721 6 Claims. (1. 189-34) Thisinvention relates to panel structures and relates more particularly topanels incorporating askin sheet and an embossed or formed sheet securedto the skin sheet to impart materially increased structural strength andrigidity thereto.

This application is a continuation-in-part of Serial Number 607,642,filed September 4, 1956, now abandoned.

It is the general object of the invention to provide a single skin sheetpanel of extraordinary rigidity and physical strength characteristics.Panels have been proposed and introduced having two-spaced externalsheets or skins of metal, or the like, and an embossed or formed sheettherebetween having special wafile patterns intended to lend rigidityand strength to the assembly and yet permit the assembly to remainrelatively light in weight. Scurlock 2,481,046 is representative of suchpanels. In these prior panel arrangements the inner rigidity impartingsheet has usually been formed or embossed to have a multiplicity ofindentations on each side providing the sheet with a plurality ofelevations at each side, terminating in flat or relatively fiat plateausor lands to which the spaced skins are secured by welding, riveting,brazing, cementing, or the like.

In such prior double-faced panels the pyramids or other elevated regionsare joined one with another by what we will term bridges and because thelands or apices of the elevated regions occupy the outermost planes ofthe embossed sheet these bridges occupy planes between said outermostplanes and usually about midway therebetween. We have found that thebridges add greatly to the rigidity of the sheet but that the locationof the bridges in areas or planes spaced between the planes to beoccupied by the skin sheets is not conducive to the development ofmaximum strength and rigidity in the panel, particularly, in the case ofsingle skin sheet panels. Therefore, it is an object of this inventionto provide panels of the class referred to having an inner orreinforcing sheet of special configuration, particularly designed toimpart greatly increased strength and rigidity to the panel.

Another object of the invehtion is to provide a panel construction ofthe class referred to wherein the angular portion or bridges join theelevated areas or projections at or occupy the plane most remote fromthe plane occupied by the lands to which the skin sheet is attached. Theangular bends or bridges joining the embossed elevations are in theplane which defines the side of the panel opposite the side to which theskin sheet is attached and are, therefore, in the most advantageouslocations from the standpoint of imparting strength and rigidity to thepanel structure.

Another object is to provide a panel of high heat transferability. Inhigh speed aircraft the skin of the panel used on the exterior surfacebecomes heated due to the friction of the air. It is, therefore,particularly advantageous to develop an exterior skin surface foraircraft which will permit the dissipation of heat.

As a solution to this problem this invention presents a structural panelwhich has excellent heat transfer properties due to the fact that airmay circulate on the back side of the skin sheet and within the spacearound the embossed projections on the embossed sheet. In presentaircraft construction panels there is no chance for this type of aircirculation to cool the skin sheet.

3,011,602 Patented Dem 5, 1961 This particular panel arrangement is,also, particularly configured to be a safe guard against explosivedecom- 'pression. If a rupture occurs in the panel it will first occurin the skin sheet and the backing sheet will then not rupture as easily,so as to permit decompression of the fuselage of the aircraft, as itwill sustain a higher stress load due to its non-planar configuration.

It is further object to provide a panel which is less expensive toconstruct and easier to shape and to work with than the presentlyemployed honeycomb panels. There are variousdifiiculties arising withthe manufacture of honeycomb panels and, in particular, bondingdifiiculties exist in bonding the honeycomb portion to the two outsideskin sheets.

Yet another object is to provide a panel having a lower weight persquare foot than the honeycomb panels in present use. A weightcomparison for steel panels constructed by the teachings of the presentinvention and by i the conventional honeycomb raised sandwich structureis the following: 7 j a The single skin sheet embossed panel of thepresent invention has a weight of from 2.3 to 2.5 lbs. per square footand the double skin honeycomb structure from 2.8 to 3.0 lbs. per squarefoot.

Other objects and features of this invention will become apparent fromthe following description of typical preferred embodiments throughoutwhich reference will be made to the accompanying drawings in which:

FIGURE 1 is a plan View of a panel constructed in accordance with theinvention with a portion of the skin sheet broken away to show theformed reinforcing sheet;

FIGURE 2 is an enlarged fragmentary vertical sectional view taken asindicated by line 2-2 on FIGURE 1;

FIGURE 3 is a fragmentary perspective view of the panel with the skinsheet and the reinforcing sheet appearing in partial cross section;

FIGURE 4 is a perspective View of a portion of the reverse or inner sideof the panel illustrating the configuration of the backing sheet andshowing portions of those sheets in cross section;

FIGURE 5 is a plan View of a modification of the planar skin sheet inwhich the skin sheet has been contoured to conform to the embossedprojections;

FIGURE 6 is a view taken on the line 6-6 of FIG- URE 5;

FIGURE 7 is a plan view of the preferred modification of the embossedpanel, in which the land portions of the panel are placed out of theplane of the paper;

FIGURE 7a is the reverse view of a panel as positioned in FIGURE 7; inthis view of the bridges portion are displaced from the plane of thepaper;

FIGURE 8 is a view taken on the line 8-8 of FIG- URE 7 FIGURE 9 is aview taken on the line 99 of FIG- URE 7;

hFIGURE 10 shows the margin portion of an embossed s eet;

FIGURE 10a is a view of the reverse side of an embossed panel with amargin portion as shown in FIG- URE l0; 7

FIGURE 11 is a view taken on the line 11-11 of FIGURE 10a;

FIGURE 12 is an enlarged fragmentary view in plan of the intersection ofthe bridges portion of the embossed sheet of FIGURES 7 through 11;

FIGURE 13 is a modification of the present invention in which aperforated skin sheet has been attached to the bridges portion of theembossed panel;

FIGURE 14 is a modification of the present invention in which aperforated skin sheet has been attached to the lands portion of theembossed sheet and a heat-resistant plastic layer has been laminated tothe skin sheet;

- 3 FIGURE shows another modification of the present invention in whicha ceramic filler material has been creased bridge thickness and aperforated and sculptured skin sheet; 7

FIGURE 17 is an alternative structure of that shown in FIGURE 16. Thismodification of the structural panel has a head of metal deposited inthe otherwise normally shaped bridge portion;

FIGURE 18 is a modification showing an orthogonal grid' attached to thebridges of the embossed panel and thereby increasing the strength ofsaid bridges area;

FIGURE '19, is a further modification of the orthogonal grid of FIGURE18; and V FIGURE '20 is yet another modification of the orthogonal gridof FIGURE 18. 7

FIGURE 21 is an enlarged and dimensioned cross section view of theembossed sheet taken on the line 88 of FIGURE 7.

FIGURE 22 is an enlarged and dimensioned cross section view of theembossed sheet taken on the line 9-9 of FIGURE 7. a

Thepanel of the invention comprises generally two sheets, namely a skinsheet and an embossed sheet or backing sheet. It will usually be foundmost desirable to form the sheets of metal, such as steel, stainlesssteel, aluminum alloy or the like, and where the panel is to be employedin aircraft constructions both sheets are preferably relatively thin.

SKIN SHEET The skin sheet (FIGURES l-4) is shown as a plane flat memberhaving parallel surfaces, it being understood the sheet 10 may be shapedor contoured as required for given applications of the panel. The shapedor contoured skin sheet shown in FIGURES 5 and 6 may be formed withsheet areas 2.1 of reduced thickness which willcontact the fiat landportions of the truncated pyramidal configurations of the embossedsheet, to be described below. Between these areas 21 are ridges or grids22. Areas 21 may be formed by such conventional processes as chemicalmilling, for example. A second modification is shown in FIGURES 13,wherein the skin sheet 52 is perforated with perforations 53. A thirdmodification of a contoured skin sheet is shown in FIGURES l6 and 17 inwhich skin sheet 67 has perforations 68 in those portions of the skinsheet not contacting the lands as does the portion 65 of the skin sheet.Perforations 68 are shown with upturned edges 69, which edges impartfurther structural rigidity to the panel as a whole.

BACKING SHEET The core sheet or backing sheet may be formed from asingle flat piece of material by embossing or pressing or plating but ispreferably configured by stretch-forming, said stretch-forming'operationbeing performed by rigidly anchoring the margin portions of the flatpieceof material to be embossed and then striking or stretching thepyramidal projections into the sheet by means of coacting dies. Thismethod of forming thus difiers from the dieshaping procedure of drawingwherein the margins of the blank being shaped are fed from the outsidetoward thecenter of theblank during the forming process. Thestretch-forming formation of the embossed panel imparts superior flexureproperties to a panel including the present embossed sheet. a

In accordance with the invention as shown in FIGURES 1 through 4, theembossed orbacking sheet 11 has a multiplicity of depressions orindentations 12 pressed or stretch-formed in one side thereof to leaveor provide a multiplicity of. projections 13 on the other side of thesheet, said depressions 12 being the underside of pro' jeetions 13.While the invention contemplates that the indentations 12 and,therefore, the projections 13 may be of selected configuration, itispreferred to make them of generally truncated pyramidal shapes.Preferably, the projections are a configuration which approximates thecombination of a truncated cone and a truncated rectangular pyramid.

FIGURES 1 through 4 show the embossed sheet having truncated rectangularpyramidal projections formed therein. indentations 1 2 and projections13 have tapered sides which converge toward the rectangular flat land14. These lands 14 are fiat and are disposed adjacent to the skin sheet10. so as to be conveniently and effectively joined to the skin sheet byriveting, welding, brazing, cementing 'or otherwise. In the drawings thenu vmeral 15 designates welds such as spot welds joining 7 ing of thelands 14 may be varied considerably, depending upon the particulargeneral proportions and appli cations of a panel, it is of coursedesirable tomake the lands sufliciently extensive to have adequateengagement with the sheet 10 and to be readily and efiectively securedthereto by the rivets, welds, cement, or the like.

The embossed or backing sheet 11 is further characterized by areas orregions which join the adjacent projections 13, which regions will betermed bridges 16. As seen in thedrawings and as best illustrated inFIGURES 2 and 4, these bridges 16 are in the nature of abrupt or sharpangled ridges or bends, The bridges 16 preferably lie in a common plane,parallel with the plane of the lands 14 and the skin sheet 10, assumingthe panel to be planar. Thus the bridges 16 join the projections 13 andoccupy the plane most remote from the sheet 10. We have found that thislocation of the flexure resisting bridges is most advantageous inimparting rigidity and structural characteristics to the compositepanel. Furthermore, by inspecting FIGURES l and 4 of the drawing, itwill be seen that the bridges 16 are joined one with another toconstitute a grid-like pattern of a multiplicity of inter-connectedsquares or diamonds positioned in diagonal or orthogonal patterns. Thisdiamond pattern of the flexure resisting bridges 16 further impartsextraordinary physical strength characteristics and flexure resistingcharacteristics to the panel.

The preferred projection configuration, shown in FIG- URES 7 through 12,is resonant between a truncated cone and a truncated rectangularpyramid-shape. These projections ar described by having a pyramidalfrustoconical configuration. The embossed backing sheet 30 hasprojections 31 of the resonant structure described having circular'lands32 disposed at the converging apices of the slightly curved sides 34;The sides 34 of the projections 31 intersect each other alongcurvilinear bends 36. The projections are joined at the bases thereof bybridges 38, which bridges intersect one another to form the intersectionof said bridges 38. The'cross section of this panel shown in FIGURE 8shows the broadest dimension of this intersection 39.

It has been found, as a practical matter, that for a one inch basedimension of the projections the maximum height to which the pyramidalprojections can be stretchedformed is approximately of an inch. A heightof /2 inch for a one inch base dimension has been found desirable forthe proper flexure characteristics of the panel. The maximum height towhich the metal can be stretchedformed without tearing is, of course, aphysical property of the metal used in the formation of the embossedsheet.

MODIFICATIONS In a modification adapted for convenient usage, theembossed sheetis formed with a margin portion around the periphery ofthe sheet. These margins may be prepared to adapt the panel for readyinstallation for various intended purposes. The margins 40, shown inFIGURES 10 and are preferably coplanar with the lands 32 of the embossedsheet 30. The skin sheet may be readily attached to the lands and to themargin portion of the sheet so as to provide an integral panel unit.This unit presents a fiat surface on both sides since the planepresented by the skin sheet and the margin portion of the embossed coresheet would present one fiat surface and a second surface would bepresented by the fiat plane of the bridge grid Work 38 and 39.

FIGURE 12 is an enlarged fragmentary view showing the intersection offour of the bridges 38 to form the rounded cornered intersection 39 ofthe embossed sheet 30. This intersection 39 is formed by the integratedintersection of the four bridges 38 as well as the lower portions of thefour curvilinear bends 36 of the four adjacent projections 31. As shown,the intersection is disposed coplanar to the flat portions of thebridges and has rounded corners due to the round cornered rectangularbase of the projections 31. The curvilinear bends of the four adjacentprojections are curved so as to de fine the sides of two normallyintersecting parabolas, which parabolas would have flattened apices aswould be formed by the planar intersection 39 of the bridges 38.

FIGURE 13 shows a modification of the present invention in which thepanel 56 is composed of skin sheet 52, formed with preforations 53,attached to the bridges portions 54 of the embossed sheet 55. This panelmodification is particularly suitable for acoustical boards or panelsfor use in aircraft, buildings, and other structures requiring panelswith sound-proofing characteristics. It is also useful as a button boardor lath board in that it is adapted to receive plaster and othersurfacing materials. In this modification the backing sheet 55 may bethe same as above described.

When intended for acoustical or sound-absorbing and damping purposes,the skin sheet 52 may be secured to the bridges 54- of the backingsheet, as illustrated in FIGURE 13, or may be secure to the lands 57 ofthe backing sheet 55, as in FIGURES l4 and 15. As shown in FIGURE 13 theperforations 53 are opposed or aligned with the lands 57. The panelshown in FIGURE 13 is especially well adapted as a plaster backing boardor lath since the plaster, or like material, when applied thereto entersthe openings 53 to form buttons behind the skin sheet 52 whicheffectively locks the plaster to the panel.

This type of panel is also well adapted for a heat insulating panel as alayer of heat-resistant plastic material may be attached to theperforated skin sheet. A modification of this type is shown in FIGURE14, wherein the panel 50a consists of embossed backing sheet 55 havingattached thereto, at the lands 57, a perforated skin sheet 52 withperforations 53 therein, and a heat-resistant plastic layer 53 attachedto the outer surface of the perforated skin sheet.

Also, as shown in FIGURE 15, the perforated panel of this modificationis easily adapted to have a ceramic material such as an insulatingceramic compound 59 poured into the perforations of the skin sheet 52and then smoothed over in a cover layer so as to provide an insulatingbuilding panel.

FIGURE 16 shows a modification of the instant invention in which thepanel 60 is composed of a special embossed panel 62 which has lands 64and a thickened bridge portion 66. Alternatively to a fiat skin sheet ashas been heretofore described in connection with various panels, acontoured skin sheet 67 may be provided for any of the embossed backingsheets. As shown in FIGURE 16 such a contoured sheet 67 has perforations63 in those portions of the skin sheet not contacting the land portions64 of the embossed sheet. These perforations 68 are shown with up turnededges 69, which edges impart further structural ridgity to the panel.

FIGURE 17 shows another modification of the present invention includinga deposite of a head of metal 70 on the inner portion of the bridges 72of the embossed 6 sheet 74 of panel 76 so that a thickened area may bepresented for resisting excess stresses placed upon the panel. Both thismodification and the modification shown in FIGURE 16 would serve thissame function in resisting excess strsses. FIGURE 17 is also shown witha contoured skin sheet which has been described in the foregoingparagraph.

A third modification is shown in FIGURES 18 through 20. In thismodification a thickening of the bridges portion of the embossed sheetis accomplished by attaching an orthogonal grid 80 to the embossed sheetwhich is attached through its lands 82 to a skin sheet 84. A slightlydifferent configuration of the orthogonal grid 80 is shown in FIGURE 19as 80a, in which the outer edges of the orthogonal grid, at each openingin the grid, are slightly downturned. FIGURE 20 shows the orthogonalgrid 80b conforming to the contour of the bridges.

The embossed sheet of FIGURE 16 may be formed by any method from a blanksheet which has an integral grid work of portions which are thicker thanthe remaining portion of the blank. This blank sheet may be formed bysuch processes as selective chemical-milling, which is a chemicaletching process to thin the metal not in the grid work, selectivemachining, or roll forging, etc.

PANEL CHARACTERISTICS The panel herein described is extremely light inWeight and yet possesses great strength in shear and in compression,both transverse and edgewise, and is highly resistant to recurringbending forces. This well adapts the panel for use in large sectionswhere it may be required to span considerable distances between supportsor framed members of the building, aircraft, or other structure in whichit is to be used.

It should also be noted that the panel described herein will havesuperior bending characteristics over the panel presently employed inthe aircraft industry, i.e. the panel may be formed into acylinder. Oncethis panel has been bent into the desired shape by the conventionaltechniques such as employing drop hammers, hydraulic presses, powerbrakes, stretch-forming machines, etc.; it will retain its structuralcharacteristics in these various shapes. In connection with the superiorbending characteristics above mentioned, the fiexure characteristics arealso outstanding as this panel will resist biaxial stretching in theevent of overloading. But upon overloading the panel will stretch withthe forces imposed upon it rather than crumbling or completelycollapsing. It has been concluded from test runs on the panel and onother various structural panels that the core configuration of thispanel gives the panel these superior properties.

The above superior properties of the panel of the instant inventionformed with the particularly configured embossed sheet are partly due totwo physical characteristics of the embossed sheet.

One of these physical characteristics of a stretch-formed embossed panelis that the thickness of the panel varies according to various positionson the embossed panel. This varying thickness is shown in FIGURE 21,which figure is an enlarged view of the cross section shown in FIGURE 8.The dimensions shown in FIGURE '21 are the dimensions resulting from thestretch-forming of a sheet blank which was originally 0.04 inch thick.As will be noted from FIGURE 21 the intersections of the bridgesportions 39 have an average thickness of .035 inch while the averagethickness of the lands portions 32 is 0.021

' inch. The curvilinear bends 36 have an ever decreasing dimension fromthe intersection of the bridges portions 39 to the edge of the landsportions 32. As the curvilinear bends begin to taper away from theintersection of the F. J is a representation of actual micrometerreadings, and thus, the variation between the various readings due tomicrometer measurement error. A second view of the embossed panelstretch-formed by the present invention is shown in FIGURE 22, whichview is a cross section similar to the cross section shown in FIGURE 9.As this figure shows, the average dimension of the bridges 38 is 0.029inch while the lands 32 have an average dimension of 0.02 inch.Intermediate the bridges and the lands are the arcuate sides 34 whichhave, from the bridges, an ever dec'reasing dimension tapering from0.032 inch to 0.011 inch at the end of the side nearest the lands 32,the

junctions of the side 34 with lands 32 have a dimension of 0.015 inch.

The percentage thinning factors at the various positions throughout theembossed panel stretch-formed as taught by this invention and as shownin FIGURES 21 and 22 may be computed by the following formula:

area thickness, inches 0.04

Table I Thinning factor Average Thickness Average Thinning FactorsPortion of Sheet Portion Intersection of bridges Bridge end of bandsCenter 01' bends. Lands end of bends Lands e- U! COCO! An importantadvantage of the stretch-forming of a sheet in accordance with thepresent invention lies in the fact that the thinning occurs in areaswhich are'of small consequence structurally, as they do not carry 'theprimary loads. It is the bridges portion which carry the primarystresses, as far as the backing sheet is concerned, and it will be notedfrom the Table I the highest average thinning factors are present in thearea of the bridges. Thus, it is concluded that by stretch-forming theembossed sheet a considerable weight saving over other forming methodsis realized, due to this thinning of the metal.

A second physical characteristic which is present in the stretch-formedembossed sheet constructed by the teachings of the present invention isthat, stretch-forming causes the embossed panel to become strainhardened in certain portions. This strain hardening further increasesthe strength of the panel. In a draw forming operation metal is fed infrom the outer periphery of the blank being so formed, which drawingreduces the amount of the stretching required to form a given sheet andthus does not allow this same strain hardening of the metal totakeplace. In connection with this strain hardening effect as astretch-forming operation the embossed panel is also left with residualstresses in certain portions of the embossed sheet and in particular,residual stressesare set up in the bridges portion of the embossedsheet.

It should be noted that this same hardening feature is of significanceonly under conditions where heat treatment following stretch-forming isnot employed, for when a panel is manufactured for high-strengthefficiency requirements the panel is subjected to heat treatment inorder that it will obtain high-strength levels.

The strain hardening and residual stresses effect of the stretch-formingoperation result particularly in causing those curved portions of theembossed panel, such as the bridges, the intersection of the bridges,the arcuate sides,

' and the curvilinear bends of the projections,-to'act as individualspring systems which are integrated through the continuity of the metalinto one continuous resilient sheet.

As has been above explained it is occasionally desirable to increase thethickness of the metal at the bridges portion of the embossed sheet.This disclosure is shown in FIGURES 16 and 17 which is shown with apreforated and contoured skin sheet 67. It should be noted that where anincreased thickness of metal is used in the bridges the skin sheet ispreferably perforated as shown in those figures so as to permit properresiliency characteristics.

While the invention has been described in connection with differentembodiments thereof, it will be'understood that it is capable of furthermodification, and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains, and as may be applied to the essentialfeatures hereinbefore set forth and as fall within the scope of theinvention or the limits of the appended claims.

Having thus described our invention what we claim is:

1. A high-strength light-weight sheet adapted for use as a panelcomponent consisting of an embossed sheet having formed therein aplurality of projections spaced in mutually adjacent relationship to oneanother in a rectangular gridwork, said projections being of a generallypyramidal frusto-conical configuration, said projection having curvedsides, said projections having a round cornered rectangular base and acircular top, said top having a planar portion and having rounded edgesconneting said planar top with said curved sides, bridgesinterconnecting the projections at their bases, the center portion ofsaid bridges being generally flat and the portion of said bridgescontacting said sides of said projections being curved, fourintersecting bridges forming a flattened intersection, said intersectionbeing disposed coplanar, with the flattened portion of said bridges, andsaid bridges occupying the plane farthest removed from the top of thesaid projections.

2. A panel as described in claim 1 wherein, said curved sides at the endof said sides nearest said bridges of said embossed sheet have a rangeof thinning factors of 0.70 to 0.80, a range of 0.20 to 0.40 in thecenter of said sides, and a range of thinning factors of 0.30 to 0.50 atthe top end of said sides, said tops having a thinning factor range of0.40 to 0.60, said bridges having a thinning factor range of 0.60 to0.85, and said intersection of said bridges having a thinning factorrange of 0.80 to 0.95.

3. A sheet as described in claim 1 wherein, said bridges have athickness of at least twice the thickness of the remainder of saidembossed sheet.

4. A sheet as described in claim 1 wherein, said projections have amaximum ratio of height dimension to base dimension of %1.

5. A sheet as described in claim 1 wherein, said curved sides of saidprojections are bowed inwardly toward the height axis of saidprojections.

6. A panel as described in claim 1 wherein, said bridges have portionsthereof which are strain hardened.

References Cited in the file of this patent UNITED STATES PATENTS

